The present invention relates to a closing unit for an injection molding machine for processing plastic material.
Closing units for injection molding machines generally have a fixed mold mounting plate, a moveable mold mounting plate, and a linkage to connect the fixed plate with the moveable plate. European Pat. No. 0 658 136 B1 discloses an exemplary closing unit for molds of injection molding machines and describes the use of an electric motor which includes a hollow shaft. A threaded spindle is received within the hollow shaft for axial movement via a nut and secured to a toggle lever system or systems so as to be constraint against rotation. This conventional closing unit suffers shortcomings because it can be operated only in a single speed range, which, moreover, operates also at a fairly low level.
European Pat. No. 0 245 517 B1 discloses a closing unit for injection molding machines, including a single-piece spindle having two threaded portions with opposite thread pitch. The nuts corresponding with the threads move relative to one another whereby a threaded portion is disengageable by a clutch from executing a rotation movement. This spindle configuration is fairly bulky as the individual threaded portions must be spaced from one another at significant distance and the spindle drive must be mounted to the end of the spindle.
It would therefore be desirable and advantageous to provide an improved closing unit for an injection molding machine, to obviate prior art shortcomings and to enable high movement speeds and thus shorter cycles at minimum energy consumption while still being reliable in operation and simple in structure.
According to one aspect of the present invention, a closing unit for use with an injection molding unit for processing plastic material includes a fixed mold mounting plate, a moveable mold mounting plate, a linkage for connecting the moveable mounting plate to the fixed mounting plate, at least two spindles arranged in series and having thread pitches configured in opposite manner, one spindle operatively connected to the fixed mounting plate, and with the other spindle connected to the linkage; a drive mechanism intended for moving the moveable mounting plate relative to the fixed mounting plate and including a sleeve-like force transmission element, which is arranged in concentric surrounding relationship to the spindles and has opposite end faces, and an electric motor operatively connected to the force transmission element; and at least two spindle nuts, one spindle nut arranged at one of the end faces of the force transmission element and interacting with the force transmission element and one of the spindles, and the other spindle nut arranged at the other end face of the force transmission element and interacting with the force transmission element and the other one of the spindles.
The present invention resolves prior art problems by providing two spindles with opposite pitch so that a rotation of the force transmission element translates in a speed that is twice as fast compared to conventional systems for closing and opening the moveable mold mounting plate.
The electric motor may be a hollow shaft motor. Suitably, the hollow shaft motor operates the force transmission element and is moveable in axial direction while constrained against rotation by an anti-rotation device. The anti-rotation device is realized by form elements, which may, for example, embrace as sleeves rods or bars of the injection molding machine, or have positively engaging members in the form of tongue and groove to provide a conjointly moving torque support.
According to another feature of the present invention, the drive of the sleeve-like force transmission element may include a stationary electric motor which has driving elements, such as gears or belts, to positively connect to the force transmission element to thereby allow an unhindered movement of the entire drive in an axial direction. In the case of a belt drive, this can be realized, e.g., by configuring the force transmission element as double sleeve in the form of an inner sleeve and an outer sleeve which are interconnected by a spline profile so that the inner sleeve can move in an axial direction, as the outer sleeve rotates while being fixed in place.
The spindles may have any desired pitch. Currently preferred, however, is the provision of an identical pitch of both spindles.
According to another feature of the present invention, there may be provided an end plate, which is connected to the fixed mounting plate, and a slip-controlled brake, which is disposed between the end plate and the one spindle for allowing rotation of the one spindle in radial direction. This spindle can hereby be operated by a further electric motor. In this way, random speeds are possible and generated clamping forces can be modified as desired, while still avoiding an inadvertent return movement of the spindle nuts relative to the spindles.
The motor-driven mechanism according to the invention is applicable for two-platen machines as well as for three-platen machines.
According to another feature of the present invention, there may be provided a protective cover, e.g. a bellows, for enveloping the spindles.